Field of Invention
This invention relates to catalytic chemical conversion of sugars comprising monosaccharides and disaccharides to ethanol at substantial yields in a single process step without fermentation. Specifically, this application discloses rapid, efficient catalytic conversion of sugar materials including sucrose, mannose, glucose, fructose and galactose in an acid medium containing inorganic sulfates comprising alkali metal, alkaline earth and other soluble metal sulfates to ethanol employing catalysts based on transition metal complexes possessing a degree of symmetry as described herein.
Description of Prior Art
The chemical process industry has grown to maturity based on petroleum feed stocks, a non-renewable resource that may become unavailable in the next 100 years. This planet Earth fosters continual growth of abundant carbohydrate based plants including fruits, vegetables, starches, grain food sources, grasses, shrubs, trees and related natural materials. Trees, corn cobs, support plant stalks, reeds and grasses are subject to catalytic digestion processes converting cellulosic materials to sugar substances whereas the present application teaches catalytic conversion of sugars to ethanol. These processes are many times faster and more efficient than fermentation processes. A major industry is blooming in ethanol production and this process is fundamental for efficient catalytic conversion of essentially all sugar materials to ethanol for use as a fuel and as a starting material in a modern chemical process industry.
Previous methods for production of ethanol include Fischer-Tropsch conversion of syntheses gas and fermentation of sugars. Fermentation of cane and beet sugar, grains and corn, as well as fermentation of sugars produced by acid digestion of wood and related plant cellulose materials constitute the majority of present production processes. Significant effort has been expended to isolate specific enzymes that may be more efficient in the fermentation process and those that might increase conversion efficiency well above ten percent. Ethanol has also been made from ethylene dissolved in sulfuric acid, diluted and isolated by distillation and by heating ethylene with steam at 300° C. and 1000 to 4000 psi pressure using acid or acidic transition metal oxide catalysts but these processes are not efficient in direct production of ethanol.
U.S. Pat. No. 4,415,749, issued Nov. 15, 1983, teaches a process converting methanol and synthesis gas to ethanol and methyl acetate in the vapor phase at 225° C. to 300° C. over zero valent Rh and Fe at 50 psig to 250 psig pressure. U.S. Pat. No. 6,747,067, issued Jun. 8, 2004, presents gasification of cellulose to carbon monoxide and hydrogen for subsequent formation of methanol, ethanol and related products. Neither of these processes start with natural sugars and ethanol is not the primary product. Ligno-cellulose biomass has been converted to sugars, then ethanol using metal salts as discussed in U.S. Pat. No. 6,660,506, issue Dec. 9, 2003. There is also a catalytic process for conversion of sugar alcohols to anhydro-sugar alcohols as disclosed in U.S. Pat. No. 4,409,404, issued Oct. 11, 1983.
U.S. Pat. No. 7,070,967, issued Jul. 4, 2006 teaches application of the flocculent strain Saccharomyces cerevisae for conversion of sugar to ethanol by fermentation. U.S. Pat. No. 4,876,196, issued Oct. 24, 1989 discloses a method of continuously producing ethanol from sugar by fermentation using Zymomonas mobilis at a pH of from 4.5 to 7 and U.S. Pat. No. 4,797,360, issued Jan. 10, 1989 offers a process for conversion of sucrose to fructose and ethanol by fermentation using Zymomonas mobilis and/or the enzyme levansucrase. These fermentation processes are slow and do not teach direct catalytic conversion of essentially any sugar to ethanol. Direct catalytic conversion of sugars to ethanol has been conducted in the temperature range of 75° C. to 250° C. as disclosed in U.S. Pat. No. 8,697,406, issued Apr. 15, 2014.
The present application discloses use of low valent mono-metal, di-metal, tri-metal and/or poly-metal backbone or molecular string type transition metal catalysts, as described in this application, for direct production of ethanol from sugar materials in the temperature range of 0° C. to 75° C. Catalytic conversion processes are not limited to a single transition metal compound or catalyst but are effective using a wide range of catalysts.